Use of pufas for treating skin inflammation

ABSTRACT

The present invention provides a compound which is a polyunsaturated fatty acid (PUFA) derivative of formula (I), 
     
       
         
         
             
             
         
       
     
     or a pharmaceutically acceptable salt, or solvate thereof, for use in treating various skin disorders.

FIELD OF THE INVENTION

The present invention relates to novel methods of treating skininflammation, in particular skin inflammation caused by atopic eczema,contact dermatitis, psoriasis or uremic pruritis.

BACKGROUND OF THE INVENTION

Most common skin disorders and complaints comprise a number of differentcomponents. Thus, many skin disorders involve (a) hyperproliferation,(b) inflammation and/or (c) dehydration. Hyperproliferation involves astate of abnormally high cell division, which can lead to excess flakingskin. Inflammation involves swelling and redness of the skin, as well assensations of increased heat, and pain in the skin. Dehydration involvesloss of water from the skin and may be due, for example, to damage tothe normally waterproof top layer of the skin (epidermis).

Inflammation of the skin (dermatitis) in mammals can result from anumber of different etiologies. Dermatitis can be caused by eczema, inparticular atopic eczema (atopic dermatitis), disseminatedneurodermatitis, flexural eczema, infantile eczema, prurigo diathsique,contact dermatitis, (eg irritant contact dermatitis, allergic contactdermatitis and photocontact dermatitis), xerotic eczema, seborrheiceczema, dyshidrosis, discoid eczema, venous eczema, dermatitisherpetiformis, neurodermatitis and autoeczematisation. Dermatitis canalso be caused by skin inflammation resulting from exposure toradiation, in particular exposure to ultraviolet radiation. Other causesof dermatitis includes uremic pruritis and autoimmune diseases, inparticular lupus and psoriasis.

Inflammation of the skin causes rashes, redness, skin edema (swelling),itching, blistering, sensations of pain and/or heat and can beunsightly. The itchiness caused by inflammation can lead to scratching.Scratching of skin that is already damaged in some way can easily leadto the barrier of the epidermis being broken, resulting in bleeding, andsecondary infection with pathogens. Such secondary infection can requiretreatment with antibiotics.

It is well known that when treating a skin condition that has a numberof different components, i.e. hyperproliferative, inflammatory and/ordehydrative components, a number of different treatments may be used.Thus, in the treatment of psoriasis, for example, anantihyperproliferative may be used to treat the hyperproliferativecomponent of the disease, an anti-inflammatory may be used to treat theinflammatory component and an emollient may be used to treat thedehydrative component.

The most common form of treatment for inflammation of the skin is oraland/or topical steroids. There are, however, drawbacks associated withsteroid treatments. Common side effects associated with steroids includestunting of growth, thinning of the skin, muscle loss and osteoporosis.

The present invention relates to new methods for treating skininflammation, in particular skin inflammation caused by atopic eczema,contact dermatitis, psoriasis or uremic pruritis, in mammals.

Eicosa-8Z,11Z,14Z-trienoic acid (Dihomo-γ-linolenic acid or DGLA) is acommercially available polyunsaturated fatty acid (PUFA). DGLA has thestructure shown below.

EP-A-0085579 describes the use of DGLA in combination with antipruriticlithium salts. EP-A-0173478 describes the use of DGLA in combinationwith anti-inflammatory glucocorticoids. In these applications, treatmentwith lithium salts and glucocorticoids is supplemented with DGLA, asboth lithium salts and glucocorticoids are believed to block release ofDGLA from endogenous stores in the body.

Advantageously, it has now been discovered that DGLA can be usedeffectively as a monotherapy.

5-Hydroxy-eicosa-6E,8Z,11Z-trienoic acid (5-HETrE)) is a commerciallyavailable PUFA derivative derived from mead acid. 5-HETrE has thestructure shown below.

8-Hydroxy-eicosa-9E,11Z,14Z-trienoic acid (8-HETrE) is a commerciallyavailable PUFA derivative derived from eicosa-8Z,11Z,14Z-trienoic acid(Dihomo-γ-linolenic acid or DGLA). 8-HETrE has the structure shownbelow.

15-Hydroxy-eicosa-8Z,11Z,13E-trienoic acid (15-HETrE) is a commerciallyavailable PUFA derivative derived from eicosa-8Z,11Z,14Z-trienoic acid(Dihomo-γ-linolenic acid or DGLA). 15-HETrE has the structure shownbelow.

15-HETrE is known to have antiproliferative properties when applieddirectly to the skin (Xi, et al; Prostaglandins, Leukotrienes andEssential Fatty Acids (2000) 62(1), 13 to 19).

13-Hydroxy-octadeca-6Z,9Z,11E-γ-trienoic acid (13-HOTrE(γ)) is acommercially available PUFA derivative derived from gamma-linolenic acid(GLA). 13-HOTrE(γ) has the structure shown below.

It has now been surprisingly found that DGLA, 5-HETrE, 8-HETrE,15-HETrE, 13-HOTrE(γ) and their derivatives are clinically useful intreating skin inflammation, in particular skin inflammation caused byatopic eczema, contact dermatitis, psoriasis or uremic pruritis, bytopical administration in mammals. A particular finding of the presentinvention is that these compounds reduce the level of COX-2 enzymes inthe skin when applied topically. The COX-2 family of enzymes have beenstrongly linked to inflammation and have been found to be present inincreased amounts in inflamed tissue.

SUMMARY OF THE INVENTION

The present invention therefore provides a compound which is apolyunsaturated fatty acid (PUFA) derivative of formula (I),

or a pharmaceutically acceptable salt, or solvate thereof, wherein

-   -   -Alk- is —CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—C₃H₆—,        —(CH₂)₃—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—,        —(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)— or        —CH₂-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—;    -   R₁ is a hydrogen atom; or    -   R₁ is a C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl, C₆-C₁₀ aryl,        5- to 10-membered heteroaryl, C₃-C₇ carbocyclyl or 5- to        10-membered heterocyclyl group; or    -   R₁ is a group of formula —CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ and        R₄ are each independently hydrogen atoms or —(C═O)—R₆, wherein        R₆ is an aliphatic group having from 3 to 29 carbon atoms; or    -   R₁ is a group of formula —(CH₂OCH₂)_(m)OH, wherein m is an        integer of from 1 to 200;    -   R₂ is a hydrogen atom; or    -   R₂ is a group —(C═O)—R₅, wherein R₅ is a C₁-C₆ alkyl, C₂-C₆        alkenyl, C₂-C₆ alkynyl, C₆-C₁₀ aryl, 5- to 10-membered        heteroaryl, C₃-C₇ carbocyclyl or 5- to 10-membered heterocyclyl        group, or R₅ is an aliphatic group having from 3 to 29 carbon        atoms; or    -   R₂ is a group of formula —(CH₂OCH₂)_(n)OH, wherein n is an        integer of from 1 to 200;        and wherein    -   said alkyl, alkenyl, alkynyl and aliphatic groups are the same        or different and are each unsubstituted or substituted with 1, 2        or 3 unsubstituted substituents which are the same or different        and are selected from halogen atoms and C₁₋C₄ alkoxy, C₂₋C₄        alkenyloxy, C₁₋C₄ haloalkyl, C₂₋C₄ haloalkenyl, C₁₋C₄        haloalkoxy, C₂₋C₄ haloalkenyloxy, hydroxyl, —SR′, and —NR′R″        groups where R′ and R″ are the same or different and represent        hydrogen or unsubstituted C₁₋C₂ alkyl;    -   said aryl, heteroaryl, carbocyclyl and heterocyclyl groups are        the same or different and are each unsubstituted or substituted        by 1, 2, 3 or 4 unsubstituted substituents which are the same or        different and are selected from halogen atoms, and cyano, nitro,        C₁₋C₄ alkyl, C₁₋C₄ alkoxy, C₂₋C₄ alkenyl, C₂₋C₄ alkenyloxy,        C₁₋C₄ haloalkyl, C₂₋C₄ haloalkenyl, C₁₋C₄ haloalkoxy, C₂₋C₄        haloalkenyloxy, hydroxyl, C₁₋C₄ hydroxyalkyl, —SW and —NR′R″        groups wherein each R′ and R″ is the same or different and        represents hydrogen or unsubstituted C₁₋C₄ alkyl;        and wherein the PUFA derivative is in the form of a racemate, a        stereoisomer or a mixture of stereoisomers,        which compound is for use in treating skin inflammation in a        mammal, by topical administration.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the results of an immunohistochemistry assay to determinethe amount of COX-2 enzymes present in ex vivo porcine ear skin 0 and 6hours after staining with diaminobenzidine.

FIG. 2 shows the results of an immunohistochemistry assay to determinethe amount of COX-2 enzymes present in ex vivo porcine ear skin, whichhas been treated with ketoprofen in fish oil, 0 and 6 hours afterstaining with diaminobenzidine.

FIG. 3 shows the results of an immunohistochemistry assay to determinethe amount of COX-2 enzymes present in ex vivo porcine ear skin, whichhas been treated with a representative compound of the invention, DGLA,0 and 6 hours after staining with diaminobenzidine.

FIG. 4 shows the results of an immunohistochemistry assay to determinethe amount of COX-2 enzymes present in ex vivo porcine ear skin, whichhas been treated with a representative compound of the invention,15-HETrE, 0 and 6 hours after staining with diaminobenzidine.

FIG. 5 shows the results of a Western Blotting analysis to determine theeffect of DGLA (second bar) and 15-HETrE (third bar) on COX-2 expressionin porcine skin relative to water (first) bar. Levels in control wereassigned a value of 100%.

Preferably the alkyl, alkenyl, alkynyl and aliphatic groups areunsubstituted or substituted with 1, 2 or 3, preferably 1 or 2, morepreferably 1, unsubstituted substituents which are the same or differentand are selected from halogen atoms and C₁₋C₄ alkoxy, hydroxyl, C₁₋C₄haloalkyl, C₂₋C₄ haloalkenyl, C₁₋C₄ haloalkyloxy and —NR′R″ wherein R′and R″ are the same or different and represent hydrogen or C₁₋C₂ alkyl.More preferred substituents are halogen, C₁₋C₄ alkoxy, hydroxyl and—NR′R″ groups where R′ and R″ are the same or different and representhydrogen or unsubstituted C₁₋C₂ alkyl. Particularly preferredsubstituents include hydroxyl and —NR′R″ groups where R′ and R″ are thesame and represent hydrogen.

When the alkyl, alkenyl, alkynyl and aliphatic groups above aresubstituted by two or three substituents, it is preferred that not morethan two substituents are selected from hydroxyl. More preferably, notmore than one substituent is selected from hydroxyl.

Most preferably, the alkyl, alkenyl and alkynyl groups above areunsubstituted.

As used herein, a C₁₋C₆ alkyl group is a linear or branched alkyl groupcontaining from 1 to 6 carbon atoms, for example a C₁₋C₄ alkyl groupcontaining from 1 to 4 carbon atoms, preferably a C₁-C₂ alkyl groupcontaining from 1 to 2 carbon atoms. Examples of C₁₋C₄ alkyl groupsinclude methyl, ethyl, n-propyl, n-butyl, butyl and t-butyl. For theavoidance of doubt, where two alkyl groups are present in a compound ofthe present invention, the alkyl groups may be the same or different.

As used herein, a C₂₋C₆ alkenyl group is a linear or branched alkenylgroup having at least one double bond of either cis or transconfiguration where applicable and containing from 2 to 6 carbon atoms,for example a C₂₋C₄ alkenyl group containing from 2 to 4 carbon atoms,such as —CH═CH₂ or —CH₂—CH═CH₂, —CH₂—CH₂—CH═CH₂, —CH₂—CH═CH—CH₃,—CH═C(CH₃)—CH₃ and —CH₂—C(CH₃)═CH₂, preferably a C₂alkenyl group having2 carbon atoms. For the avoidance of doubt, where two alkenyl groups arepresent in a compound of the present invention, they may be the same ordifferent.

As used herein, a C₂₋C₆ alkynyl group is a linear or branched alkynylgroup containing from 2 to 6 carbon atoms, for example a C₂₋C₄ alkynylgroup containing from 2 to 4 carbon atoms, preferably a C₂ alkynyl groupcontaining 2 carbon atoms. Exemplary alkynyl groups include —C≡H or—CH₂—C≡H, as well as 1- and 2-butynyl, 2-methyl-2-propynyl, 2-pentynyl,3-pentynyl, 4-pentynyl, 2-hexynyl, 3-hexynyl, 4-hexynyl and 5-hexynyl.For the avoidance of doubt, where two alkynyl groups are present in acompound of the present invention, they may be the same or different.

Preferably, said C₁₋C₆ alkyl group is a C₁-C₂ alkyl group, said C₂₋C₆alkenyl group is a C₂ alkenyl group and said C₂₋C₆ alkynyl group is a C₂alkynyl group.

As used herein, a halogen atom is chlorine, fluorine, bromine or iodine.

As used herein, a C₁₋C₆ alkoxy group or C₂₋C₆ alkenyloxy group istypically a said C₁₋C₆ alkyl (e.g. a C₁₋C₄ alkyl) group or a said C₂₋C₆alkenyl (e.g. a C₂₋C₄ alkenyl) group respectively which is attached toan oxygen atom.

A haloalkyl, haloalkenyl, haloalkoxy or haloalkenyloxy group istypically a said alkyl, alkenyl, alkoxy or alkenyloxy group respectivelywhich is substituted by one or more said halogen atoms. Typically, it issubstituted by 1, 2 or 3 said halogen atoms. Preferred haloalkyl andhaloalkoxy groups include perhaloalkyl and perhaloalkoxy groups, such as—CX₃ and —OCX₃ wherein X is a said halogen atom, for example chlorineand fluorine.

As used herein, a C₁₋C₄ alkylthio or C₂₋C₄ alkenylthio group istypically a said C₁₋C₄alkyl group or a C₂₋C₄ alkenyl group respectivelywhich is attached to a sulphur atom, for example —S—CH₃.

As used herein, a C₁₋C₄ hydroxyalkyl group is a C₁₋C₄ alkyl groupsubstituted by one or more hydroxy groups. Typically, it is substitutedby one, two or three hydroxy groups. Preferably, it is substituted by asingle hydroxy group.

As used herein, a C₆₋C₁₀ aryl group is a monocyclic or polycyclic,preferably monocyclic, aromatic ring containing from 6 to 10 carbonatoms, for example a C₆ aryl group containing 6 carbon atoms. Examplesof such aryl groups include phenyl, naphthalene and azulene. Phenyl ispreferred.

As used herein, a 5- to 10-membered heteroaryl group is a monocyclic orpolycyclic, preferably monocyclic, 5- to 10-membered aromatic ring, suchas a 5- or 6-membered ring, containing at least one heteroatom, forexample 1, 2, 3 or 4 heteroatoms, selected from O, S and N. When thering contains 4 heteroatoms these are preferably all nitrogen atoms.Examples include thienyl, furyl, pyrrolyl, imidazolyl, thiazolyl,isothiazolyl, pyrazolyl, oxazolyl, isoxazolyl, triazolyl, thiadiazolyl,oxadiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyland tetrazolyl groups. Thienyl, pyrrolyl, imidazolyl, thiazolyl,isothiazolyl, pyrazolyl, oxazolyl, isoxazolyl, triazolyl, pyridinyl,pyridazinyl, pyrimidinyl and pyrazinyl groups are preferred, e.g.pyrrolyl, imidazolyl, thiazolyl, isothiazolyl, pyrazolyl, oxazolyl,isoxazolyl, triazolyl, pyridinyl, pyridazinyl, pyrimidinyl and pyrazinylgroups. More preferred groups are thienyl, pyridinyl, pyridazinyl,pyrimidinyl, pyrazinyl, pyrrolyl and triazinyl, e.g. pyridinyl,pyridazinyl, pyrimidinyl, pyrazinyl, pyrrolyl and triazinyl, mostpreferably pyridinyl.

As used herein, a 5- to 10-membered heterocyclyl group is anon-aromatic, saturated or unsaturated monocyclic or polycyclic,preferably monocyclic, C₅₋₁₀ carbocyclic ring in which one or more, forexample 1, 2, 3 or 4, of the carbon atoms are replaced with a moietyselected from N, O, S, S(O) and S(O)₂, and wherein one or more of theremaining carbon atoms is optionally replaced by a group —C(O)— or—C(S)—. When one or more of the remaining carbon atoms is replaced by agroup —C(O)— or —C(S)—, preferably only one or two (more preferably two)such carbon atoms are replaced. Typically, the 5- to 10-memberedheterocyclyl ring is a 5- to 6-membered ring.

Suitable heterocyclyl groups include azetidinyl, oxetanyl, thietanyl,pyrrolidinyl, imidazolidinyl, oxazolidinyl, isoxazolidinyl,thiazolidinyl, isothiazolidinyl, tetrahydrofuranyl, tetrahydrothienyl,tetrahydropyranyl, tetrahydrothiopyranyl, dithiolanyl, dioxolanyl,pyrazolidinyl, piperidinyl, piperazinyl, hexahydropyrimidinyl,methylenedioxyphenyl, ethylenedioxyphenyl, thiomorpholinyl,S-oxo-thiomorpholinyl, S,S-dioxo-thiomorpholinyl, morpholinyl,1,3-dioxolanyl, 1,4-dioxolanyl, trioxolanyl, trithianyl, imidazolinyl,pyranyl, pyrazolinyl, thioxolanyl, thioxothiazolidinyl,1H-pyrazol-5-(4H)-onyl, 1,3,4-thiadiazol-2(3H)-thionyl, oxopyrrolidinyl,oxothiazolidinyl, oxopyrazolidinyl, succinimido and maleimido groups andmoieties. Preferred heterocyclyl groups are pyrrolidinyl,imidazolidinyl, oxazolidinyl, isoxazolidinyl, thiazolidinyl,isothiazolidinyl, tetrahydrofuranyl, tetrahydrothienyl,tetrahydropyranyl, tetrahydrothiopyranyl, dithiolanyl, dioxolanyl,pyrazolidinyl, piperidinyl, piperazinyl, hexahydropyrimidinyl,thiomorpholinyl and morpholinyl groups and moieties.

For the avoidance of doubt, although the above definitions of heteroaryland heterocyclyl groups refer to an “N” moiety which can be present inthe ring, as will be evident to a skilled chemist the N atom will beprotonated (or will carry a substituent as defined below) if it isattached to each of the adjacent ring atoms via a single bond.

As used herein, a C₃₋C₇ carbocyclic group is a non-aromatic saturated orunsaturated hydrocarbon ring having from 3 to 7 carbon atoms. Preferablyit is a saturated or mono-unsaturated hydrocarbon ring (i.e. acycloalkyl moiety or a cycloalkenyl moiety) having from 3 to 7 carbonatoms, more preferably having from 3 to 6 carbon atoms. Examples includecyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl and theirmono-unsaturated variants, more particularly cyclopentyl and cyclohexyl.A C₃₋C₇ carbocyclyl group also includes C₃₋C₇ carbocyclyl groupsdescribed above but wherein one or more ring carbon atoms are replacedby a group —C(O)—. More preferably, 0, 1 or 2 ring carbon atoms (mostpreferably 0) are replaced by —C(O)—. Most preferably, said C₃₋C₇carbocyclyl group is cyclohexyl.

Typically the aryl, heteroaryl, heterocyclyl and carbocyclyl groups inR₁ and R₅ are unsubstituted or substituted by 1, 2, 3 or 4 unsubstitutedsubstituents, for example by 1, 2 or 3 unsubstituted substituents.Preferred substituents include halogen atoms and C₁₋C₄ alkyl, C₂₋C₄alkenyl, C₁₋C₄ alkoxy, C₂₋C₄ alkenyloxy, C₁₋C₄ haloalkyl, C₂₋C₄haloalkenyl, C₁₋C₄ haloalkoxy, C₂₋C₄ haloalkenyloxy, hydroxyl, mercapto,cyano, nitro, C₁₋C₄ hydroxyalkyl, C₂₋C₄ hydroxyalkenyl, C₁₋C₄ alkylthio,C₂₋C₄ alkenylthio and —NR′R″ groups wherein each R′ and R″ is the sameor different and represents hydrogen or C₁₋C₄ alkyl. More preferredsubstituents include halogen atoms and unsubstituted C₁₋C₄ alkyl, C₁₋C₄alkoxy, hydroxyl, C₁₋C₄ haloalkyl, C₁₋C₄ haloalkoxy, C₁₋C₄ hydroxyalkyl,cyano, nitro, —SR′ and —NR′R″ groups where R′ and R″ are the same ordifferent and represent hydrogen or unsubstituted C₁₋C₂ alkyl. Morepreferred substituents include halogen atoms, hydroxyl groups and C₁₋C₂alkyl and C₁₋C₂alkoxy groups.

Most preferably, the aryl, heteroaryl, heterocyclyl and carbocyclylgroups above are unsubstituted.

When the aryl, heteroaryl, heterocyclyl and carbocyclyl groups in R₁ andR₅ are substituted by two, three or four substituents, it is preferredthat not more than two substituents are selected from hydroxyl, cyanoand nitro. More preferably, not more than one substituent is selectedfrom hydroxyl, cyano and nitro.

As used herein, a pharmaceutically acceptable salt is a salt with apharmaceutically acceptable acid or base. Pharmaceutically acceptableacids include both inorganic acids such as hydrochloric, sulphuric,phosphoric, diphosphoric, hydrobromic or nitric acid and organic acidssuch as citric, fumaric, maleic, malic, ascorbic, succinic, tartaric,benzoic, acetic, methanesulphonic, ethanesulphonic, benzenesulphonic orp-toluenesulphonic acid. Pharmaceutically acceptable bases includealkali metal (e.g. sodium or potassium) and alkali earth metal (e.g.calcium or magnesium) hydroxides and organic bases such as alkyl amines,aralkyl amines and heterocyclic amines.

The term “solvate” refers to a complex or aggregate formed by one ormore molecules of a solute, i.e. compounds of the invention orpharmaceutically-acceptable salts thereof, and one or more molecules ofa solvent. Such solvates are typically crystalline solids having asubstantially fixed molar ratio of solute and solvent. Representativesolvents include by way of example, water, methanol, ethanol,isopropanol, acetic acid, and the like. When the solvent is water, thesolvate formed is a hydrate.

The compounds of the invention may contain a chiral center. Accordingly,they can be used in the form of a racemic mixture, an enantiomer, or amixture enriched in one or more stereoisomer. The scope of the inventionas described and claimed encompasses the racemic forms of the compoundsof the invention as well as the individual enantiomers, andstereoisomer-enriched mixtures.

It will be appreciated that the term “or a pharmaceutically acceptablesalt or solvate thereof” is intended to include all permutations ofsalts and solvates, such as solvates of pharmaceutically-acceptablesalts of compounds of the invention.

R₅ and R₆ may be an aliphatic group having 3 to 29 carbon atoms.Typically, the aliphatic group is not cyclic. The aliphatic group istypically linear or branched, preferably linear. Typically the aliphaticgroup has 7 to 25 carbon atoms, more preferably 11 to 25 carbon atoms.The aliphatic group is typically unsubstituted or substituted with onehydroxyl group. The aliphatic group is preferably unsubstituted.

Aliphatic groups may be saturated, monounsaturated or polyunsaturated.Saturated aliphatic groups are preferred.

Typically, saturated aliphatic groups have from 7 to 25 carbon atoms,preferably 11 to 17 carbon atoms.

Monounsaturated aliphatic groups typically contain a single C═C doublebond. The double bond has cis or trans configuration. The single doublebond may be present at any point in the aliphatic group, but istypically 7 or 9 carbon atoms from the end of the aliphatic group distalto the (C═O) group to which the aliphatic group is attached. Typically,monounsaturated aliphatic groups have from 7 to 25 carbon atoms,preferably 15 to 23 carbon atoms.

Polyunsaturated aliphatic groups typically contain two or more C═Cdouble bonds, for example 2, 3, 4, 5 or 6 C═C double bonds. Each doublebond may have cis or trans configuration. The double bonds may bepresent at any point in the aliphatic chain, but typically, the C═Cdouble bond furthest from the (C═O) group to which the aliphatic groupis attached is 3, 6 or 9 carbon atoms from the end of the aliphaticgroup distal to the (C═O) group to which the aliphatic group isattached. Typically, polyunsaturated aliphatic groups have from 7 to 25carbon atoms, preferably 15 to 23 carbon atoms.

Typically, said aliphatic group is the group R, wherein R—CO₂H is afatty acid. Preferably, said fatty acid is lauric acid, myristic acid,palmitic acid, stearic acid palmitoleic acid, cis-vaccenic acid, oleicacid, eicosenoic acid, erucic acid, nervonic acid, alpha-linolenic acid,stearidonic acid, eicosatrienoic acid, eicosatetraenoic acid,eicosapentaenoic acid, docosapentaenoic acid, docosahexaenoic acid,tetracosapentaenoic acid, tetracosahexaenoic acid, linoleic acid,gamma-linolenic acid, eicosadienoic acid, dihommo-gamma-linolenic acid,arachidonic acid, docosadienoic acid, adrenic acid, docosapentaenoicacid, or mead acid. More preferably, said fatty acid is lauric acid,myristic acid, palmitic acid, or stearic acid.

In one embodiment, the aliphatic group having 3 to 29 carbon atoms isthe aliphatic group of a PUFA derivative of formula (I) as definedherein, i.e. the aliphatic group is of formula —(CH₂)₃-Alk-(CH₂)₄CH₃,wherein -Alk- is as defined herein.

In a preferred embodiment, the aliphatic group having 3 to 29 carbonatoms is the aliphatic group of dihommo-gamma-linolenic acid or15-hydroxyeicosatrienoic acid, i.e. the aliphatic group is—(CH₂)₆—CH═CH—CH₂—CH═CH—CH₂—CH═CH—(CH₂)₄CH₃, wherein all of the C═Cdouble bonds have cis configuration, or—(CH₂)₆-[cis]CH═CH—CH₂—[cis]CH═CH-[trans]CH═CH—CH(OH)—(CH₂)₄CH₃.Preferably, the aliphatic group having 3 to 29 carbon atoms is thealiphatic group of 15-hydroxyeicosatrienoic acid, i.e. the aliphaticgroup is—(CH₂)₆-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OH)—(CH₂)₄CH₃.

In a more preferred embodiment, the PUFA derivative of formula (I) is offormula R′(C═O)O—CH₂—CH(O(C═O)R′)—CH₂—O(C═O)R′, wherein each R′ is thealiphatic group of 15-hydroxyeicosatrienoic acid, i.e. R′ is—(CH₂)₆-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OH)—(CH₂)₄CH₃. Thus,the PUFA derivative of formula (I) is preferably

It is to be understood that the left hand side of the -Alk- moiety isbonded to the unsaturated carbon chain bearing the —COOR₁ moiety and theright hand side of the -Alk- group is bonded to the saturated carbonchain.

Typically, -Alk- is—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—C₃H₆—,—(CH₂)₃—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—, or—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—. Preferably,-Alk- is —(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH—CH₂-[cis]CH═CH—.

Typically, R₁ is a hydrogen atom; or R₁ is a C₁-C₄ alkyl, C₂-C₄ alkenyl,C₂-C₄ alkynyl, C₆ aryl, 5- to 6-membered heteroaryl, C₃-C₆ carbocyclylor 5- to 6-membered heterocyclyl group; or R₁ is a group of formula—CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ and R₄ are as defined herein; or R₁is a group of formula —(CH₂OCH₂)_(m)OH, wherein m is as defined herein,wherein said alkyl, alkenyl and alkynyl groups are the same or differentand are each unsubstituted or substituted with 1, or 2 unsubstitutedsubstituents which are the same or different and are selected fromhalogen atoms, C₁₋C₄ alkoxy, hydroxyl, and —NR′R″ groups where R′ and R″are the same or different and represent hydrogen or unsubstituted C₁₋C₂alkyl; and said aryl, heteroaryl, carbocyclyl and heterocyclyl groupsare the same or different and are each unsubstituted or substituted by1, 2 or 3 unsubstituted substituents which are the same or different andare selected from halogen atoms, and cyano, nitro, C₁₋C₄ alkyl, C₁₋C₄alkoxy, and —NR′R″ groups wherein each R′ and R″ is the same ordifferent and represents hydrogen or unsubstituted C₁₋C₂ alkyl group.

Preferably, R₁ is a hydrogen atom; or R₁ is an unsubstituted C₁-C₄ alkylgroup; or R₁ is a group of formula —CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃and R₄ are as defined herein; or R₁ is a group of formula—(CH₂OCH₂)_(m)OH, wherein m is as defined herein.

More preferably, R₁ is a hydrogen atom; or R₁ is a group of formula—CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ and R₄ are as defined herein, andwherein at least one of R₃ or R₄ is —(C═O)—R₆, wherein R₆ is as definedherein.

Most preferably, R₁ is a hydrogen atom.

m is typically an integer of from 5 to 150, preferably from 10 to 50.

R₃ is typically —(C═O)—R₆, wherein R₆ is as defined herein.

R₄ is typically —(C═O)—R₆, wherein R₆ is as defined herein.

Preferably, both R₃ and R₄ are —(C═O)—R₆, wherein each R₆ may be thesame or different and is as defined herein.

Typically, when R₃ and R₄ are both —(C═O)—R₆, then R₅ is not analiphatic group having 3 to 29 carbon atoms.

R₆ is an aliphatic group having from 3 to 29 carbon atoms, as definedherein. Typically, said aliphatic group is saturated. Typically, R₆ isan aliphatic group having 7 to 25 carbon atoms, preferably 11 to 17carbon atoms. Preferably, R₆ is a group R, wherein R—CO₂H is auric acid,myristic acid, palmitic acid, or stearic acid.

Typically, R₂ is a hydrogen atom; or R₂ is a group —(C═O)—R₅, wherein R₅is a C₁-C₄ alkyl, C₂-C₄ alkenyl, C₂-C₄ alkynyl, C₆ aryl, 5- to6-membered heteroaryl, C₃-C₆ carbocyclyl or 5- to 6-memberedheterocyclyl group, or R₅ is an aliphatic group having from 3 to 29carbon atoms; or R₂ is a group of formula —(CH₂OCH₂)_(n)OH, wherein n isas defined herein, wherein said alkyl, alkenyl and alkynyl groups arethe same or different and are each unsubstituted or substituted with 1,or 2 unsubstituted substituents which are the same or different and areselected from halogen atoms, C₁₋C₄ alkoxy, hydroxyl, and —NR′R″ groupswhere R′ and R″ are the same or different and represent hydrogen orunsubstituted C₁₋C₂ alkyl; and said aryl, heteroaryl, carbocyclyl andheterocyclyl groups are the same or different and are each unsubstitutedor substituted by 1, 2 or 3 unsubstituted substituents which are thesame or different and are selected from halogen atoms, and cyano, nitro,C₁₋C₄ alkyl, C₁₋C₄alkoxy, and —NR′R″ groups wherein each R′ and R″ isthe same or different and represents hydrogen or unsubstituted C₁₋C₂alkyl group.

Preferably, R₂ is a hydrogen atom; or R₂ is a group —(C═O)—R₅, whereinR₅ is unsubstituted C₁-C₄ alkyl; or R₂ is a group —(C═O)—R₅, wherein R₅is an aliphatic group having from 3 to 29 carbon atoms; or R₂ is a groupof formula —(CH₂OCH₂)_(n)OH, wherein n is as defined herein.

More preferably, R₂ is a hydrogen atom; or R₂ is a group —(C═O)—R₅,wherein R₅ is an aliphatic group having from 3 to 29 carbon atoms; or R₂is a group of formula —(CH₂OCH₂)_(n)OH, wherein n is as defined herein.

Most preferably, R₂ is a hydrogen atom.

n is typically an integer of from 5 to 150, preferably from 10 to 50.

When R₅ is an aliphatic group having 3 to 29 carbon atoms, saidaliphatic group is as defined herein. Typically, said aliphatic group issaturated. Typically, R₅ is an aliphatic group having 7 to 25 carbonatoms, preferably 11 to 17 carbon atoms. Preferably, R₅ is a group R,wherein R—CO₂H is auric acid, myristic acid, palmitic acid, or stearicacid.

In one embodiment, the PUFA derivative of formula (I) is present as aracemic mixture of the R and S enantiomers.

In another embodiment, the PUFA derivative of formula (I) is present asthe R enantiomer.

In another embodiment, the PUFA derivative of formula (I) is present asthe S enantiomer.

Typically, the mammal is a human.

In a preferred embodiment, -Alk- is—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—C₃H₆—,—(CH₂)₃—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—, or—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—; R₁ is ahydrogen atom, an unsubstituted C₁-C₄ alkyl group, or a group of formulaCH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ and R₄ are each independently hydrogenatoms or —(C═O)—R₆, wherein R₆ is a linear aliphatic group having from11 to 25 carbon atoms, which aliphatic group is unsubstituted orsubstituted with one hydroxyl group, or R₁ is a group of formula—(CH₂OCH₂)_(m)OH, wherein m is an integer of from 5 to 150; and R₂ is ahydrogen atom, a group —(C═O)—R₅, wherein R₅ is unsubstituted C₁-C₄alkyl, or a group —(C═O)—R₅, wherein R₅ is a linear aliphatic grouphaving from 11 to 25 carbon atoms, which aliphatic group isunsubstituted or substituted with one hydroxyl group; or R₂ is a groupof formula —(CH₂OCH₂)_(n)OH, wherein n is an integer of from 5 to 150.

In a more preferred embodiment, -Alk- is—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—; R₁ is ahydrogen atom, an unsubstituted C₁-C₄ alkyl group, or a group of formula—CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ and R₄ are each independentlyhydrogen atoms or —(C═O)—R₆, wherein R₆ is a linear aliphatic grouphaving from 11 to 25 carbon atoms, which aliphatic group isunsubstituted or substituted with one hydroxyl group, or R₁ is a groupof formula —(CH₂OCH₂)_(m)OH, wherein m is an integer of from 5 to 150;and R₂ is a hydrogen atom, a group —(C═O)—R₅, wherein R₅ isunsubstituted C₁-C₄ alkyl, or a group —(C═O)—R₅, wherein R₅ is a linearaliphatic group having from 11 to 25 carbon atoms, which aliphatic groupis unsubstituted or substituted with one hydroxyl group; or R₂ is agroup of formula —(CH₂OCH₂)_(n)OH, wherein n is an integer of from 5 to150.

In a most preferred embodiment, -Alk- is—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—; R₁ is ahydrogen atom, a group of formula —CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ andR₄ are each independently hydrogen atoms or —(C═O)—R₆, wherein R₆ is anunsubstituted linear, saturated aliphatic group having from 11 to 17carbon atoms, and wherein at least one of R₃ or R₄ is —(C═O)—R₆; and R₂is a hydrogen atom, or a group —(C═O)—R₅, wherein R₅ is an unsubstitutedlinear, saturated aliphatic group having from 11 to 17 carbon atoms, orR₂ is a group of formula —(CH₂OCH₂)_(n)OH, wherein n is an integer offrom 10 to 50.

Typically, in the compounds of the present invention, including thepreferred embodiments set out above, (a) R₁ is a group of formula—CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ and R₄ each independently represent ahydrogen atom or —(C═O)—R₆, wherein R₆ is a saturated aliphatic grouphaving from 3 to 29 carbon atoms, wherein at least one of R₃ or R₄ is—(C═O)—R₆; or

(b) R₁ is a group of formula —(CH₂OCH₂)_(m)OH, wherein m is as definedherein; and/or

(c) R₂ is a group —(C═O)—R₅, wherein R₅ is a saturated aliphatic grouphaving from 3 to 29 carbon atoms; or

(d) R₂ is a group of formula —(CH₂OCH₂)_(n)OH, wherein n is as definedherein. Such compounds will be particularly lipophilic, which isadvantageous in some instances.

In this preferred embodiment, preferably (a) R₁ is a group of formula—CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ and R₄ are each independentlyhydrogen atoms or —(C═O)—R₆, wherein R₆ is a saturated aliphatic grouphaving 3 to 29 carbon atoms, wherein at least one of R₃ or R₄ is—(C═O)—R₆; and/or (c) R₂ is a group —(C═O)—R₅, wherein R₅ is a saturatedaliphatic group having 3 to 29 carbon atoms.

In a more preferred embodiment, both R₁ and R₂ are hydrogen atoms.

In a particularly preferred embodiment, -Alk- is—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—, and R₁ and R₂are both hydrogen atoms. In this embodiment, the PUFA derivative offormula (I) is 15-HETrE and is represented by the formula

Typically, compounds of the invention are administered as one or moretreatments per day, preferably from 1 to 4 treatments per day, morepreferably from 1 to 2 treatments per day.

Typically, compounds of the invention are administered at a daily dosageof from 0.1 mg/m²/day to 1 kg/m²/day, preferably from 1 mg/m²/day to 100g/m²/day, more preferably from 10 mg/m²/day to 10 g/m²/day, mostpreferably from 100 mg/m²/day to 1 g/m²/day.

Skin inflammation includes rashes, hives, blisters and/or wheals and maybe caused by eczema, exposure to radiation, automimmune diseases, and/oruremic pruritis.

In a preferred embodiment, the skin inflammation is caused by atopiceczema, contact dermatitis, psoriasis or uremic pruritis.

In a further preferred embodiment, the skin inflammation is caused byexposure of the skin to electromagnetic radiation. This includes, forexample, exposure to sunlight, heat, X-rays or radioactive materials.Thus, in this embodiment, the compound of the present invention istypically used to treat sunburn.

The term eczema is applied to a wide range of skin conditions with avariety of aetiologies. In general, eczema is categorised byinflammation of the epidermis. Common symptoms associated with eczemainclude dryness, recurring skin rashes, redness, skin edema (swelling),itching, dryness, crusting, flaking, blistering, cracking, oozing, andbleeding. Eczema includes atopic eczema (atopic dermatitis), contactdermatitis, xerotic eczema, seborrhoeic dermatitis, dyshydrosis, discoideczema, venous eczema, dermatitis herpetiformus, neurodermatitis, andautoeczematisation. Eczema is typically atopic eczema or contactdermatitis.

Atopic eczema is primarily aggravated by contact with or intake ofallergens, which include animal hair and dander, food allergens, forexample nuts or shellfish, or drugs, for example penicillin.

Contact dermatitis includes allergic contact dermatitis, irritantcontact dermatitis and photocontact dermatitis.

Electromagnetic radiation includes radio waves, microwaves, terahertzradiation, infrared radiation, visible light, ultraviolet radiation,X-rays and gamma rays. Electromagnetic radiation is preferably infraredradiation, visible light, ultraviolet radiation, X-rays and gamma rays,more preferably ultraviolet radiation, X-rays and gamma rays.

Autoimmune diseases can involve an autoimmune response against the skin.Examples of such autoimmune diseases are lupus and psoriasis.

Uremic pruritis is a disorder of the skin associated with chronic renalfailure. It also frequently affects patients undergoing dialysistreatment.

Typically, the compound of the present invention is co-administered witha corticosteroid.

Suitable corticosteroids to be used for co-administration with compoundsof the invention are clobetasol diproprionate, betamethasonediproprionate, halbetasol proprionate, diflorasone diacetate,fluocinonide, halcinonide, amcinonide, desoximetasone, triamcinoloneacetonide, mometasone furoate, fluticasone proprionate, fluocinoloneacetonide, hydrocortisone valerate, hydrocortisone butyrate,triamcinalone acetonide, desonide, prednicarbate, prednisolone,methylprednisolone, dexamethasone, naflocort, deflazacort, halopredoneacetate, budesonide, beclomethasone dipropionate, hydrocortisone,clocortolone pivalate, methylprednisolone aceponate, dexamethasonepalmitoate, tipredane, hydrocortisone aceponate, alclometasonedipropionate, halometasone, methylprednisolone suleptanate, rimexolone,prednisolone farnesylate, ciclesonide, deprodone propionateloteprednoletabonate, betamethasone butyrate propionate, flunisolide, prednisone,dexamethasone sodium phosphate, triamcinolone, betamethasone17-valerate, betamethasone, betamethasone dipropionate, hydrocortisoneacetate, hydrocortisone sodium succinate, prednisolone sodium phosphateand hydrocortisone probutate.

Preferred corticosteroids corticosteroids to be used forco-administration with compounds of the invention are clobetasoldiproprionate, betamethasone diproprionate, halbetasol proprionate,diflorasone diacetate, fluocinonide, halcinonide, amcinonide,desoximetasone, triamcinolone acetonide, mometasone furoate, fluticasoneproprionate, fluocinolone acetonide, hydrocortisone valerate,hydrocortisone butyrate, triamcinalone acetonide, desonide, andprednicarbate.

Any reference to corticosteroids within the scope of the presentinvention includes a reference to salts or derivatives thereof which maybe formed from the corticosteroids. Examples of possible salts orderivatives include: sodium salts, sulphobenzoates, phosphates,isonicotinates, acetates, propionates, dihydrogen phosphates,palmitates, pivaiates, farnesylates, aceponates, suleptanates,prednicarbates, furoates or acetonides. In some cases thecorticosteroids may also occur in the form of their hydrates.

It is a particular finding of the present invention thatco-administration of a compound of the present invention with acorticosteroid enables the amount of corticosteroid administered to bereduced, without reducing the efficacy of the treatment. Thus, in apreferred embodiment, the compound of the present invention isco-administered with a corticosteroid, wherein the corticosteroid isadministered at a daily dosage of 50% or less, preferably 25% or less,more preferably 10% or less, most preferably 5% or less, of therecommended daily dosage of said corticosteroid in said mammal.

The person skilled in the art is well aware of the recommended dailydosages of corticosteroids in mammals. For example, the recommendeddaily dosage of hydrocortisone in humans is approximately 0.35 g/m²/day.The recommended daily dosage of clobetasol proprionate in humans is0.009 to 0.018 g/m²/day.

Thus, compounds of the present invention are typically coadministeredwith hydrocortisone, wherein the daily dosage of hydroxortisone is 0.175g/m²/day or less, preferably 0.0875 g/m²/day or less, more preferably0.035 g/m²/day, most preferably 0.0175 g/m²/day or less. Compounds ofthe present invention are typically coadministered with clobetasolproprionate, wherein the daily dosage of clobetasol proprionate is 0.009g/m²/day or less, preferably 0.0045 g/m²/day or less, more preferably0.0018 g/m²/day or less, most preferably 0.0009 g/m²/day or less.

The compounds of the present invention are typically coadministered witha further therapeutic agent, which is not a corticosteroid, which iseffective in treating skin conditions/diseases. Such therapeutic agentsare well known to the skilled person and include, but are not limitedto, immunomodulators, antiobiotics, immunosuppressants and anti-itchdrugs.

Compounds of the invention are typically commercially available, or maybe prepared by analogy with known methods. Thus, for example, both DGLAand 15-HETrE are commercially available. These available fatty acids caneasily be derivatised to obtain PUFA derivatives of formula (I) by knownmethods.

For example, PUFA derivatives of formula (I) as defined herein, whereinR₁ is a C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl, C₆-C₁₀ aryl, 5- to10-membered heteroaryl, C₃-C₇ carbocyclyl or 5- to 10-memberedheterocyclyl group; or R₁ is a group of formula —CH₂—CH(OR₃)—CH₂—(OR₄),wherein R₃ and R₄ are as defined herein; or R₁ is a group of formula—(CH₂OCH₂)_(m)OH, wherein m is as defined herein, can be prepared byesterifying a compound of formula

wherein -Alk- is as defined herein and X is a leaving group, for examplea halogen atom, a tosylate or mesylate group with an alcohol of formulaR₁′—OH, wherein R₁′ is a C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl,C₆-C₁₀ aryl, 5- to 10-membered heteroaryl, C₃-C₇ carbocyclyl or 5- to10-membered heterocyclyl group; or R₁′ is a group of formula—CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ and R₄ are as defined herein; or R₁′is a group of formula —(CH₂OCH₂)_(m)OH, wherein m is as defined herein,to obtain a PUFA derivative of formula (I) as defined herein.Alternatively, X may be a hydroxyl group. In that case, the reaction ispreferably carried out under acidic conditions, or in the presence of asuitable catalyst, for example pyridine. Compounds of formula R₁′-OH aretypically commercially available or may be prepared by analogy withknown methods.

When -Alk- is —CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—C₃—H₆—,—(CH₂)₃—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—, or—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—, PUFAderivatives of formula (I) as defined herein, wherein R₂ is a group—(C═O)—R₅, wherein R₅ is a C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl, aC₆-C₁₀ aryl, a 5- to 10-membered heteroaryl, a C₃-C₇ carbocyclyl or a 5-to 10-membered heterocyclyl group, or R₅ is an aliphatic group havingfrom 3 to 29 carbon atoms, can be prepared by treating a compound offormula (I) as defined herein, wherein -Alk- is—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—C₃H₆—,—(CH₂)₃—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—, or—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—, and R₂ is ahydrogen atom, with a carboxylic acid derivative Y—(C═O)—R′₅, whereinR′₅ is a C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl, a C₆-C₁₀ aryl, a 5-to 10-membered heteroaryl, a C₃-C₇ carbocyclyl or a 5- to 10-memberedheterocyclyl group, or R′₅ is an aliphatic group having from 3 to 29carbon atoms, and Y is a leaving group, for example a halogen atom, atosylate or mesylate group. Compounds of formula Y—(C═O)—R′₅ aretypically commercially available or may be prepared by analogy withknown methods.

When -Alk- is —CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—C₃—H₆—,—(CH₂)₃—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—, or—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—, PUFAderivatives of formula (I) as defined herein, wherein R₂ is a group offormula —(CH₂OCH₂)—OH, wherein n is as defined herein, can be preparedby treating a compound of formula (I) as defined herein, wherein -Alk-is —CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—C₃H₆—,—(CH₂)₃—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—, or—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—, and R₂ is ahydrogen atom, with a compound of formula Z—(CH₂OCH₂)_(n)OH, wherein nis as defined herein and Z is a good leaving group, for example ahalogen atom, a tosylate or mesylate group. Compounds of formulaZ—(CH₂OCH₂)_(n)OH are typically commercially available or may beprepared by analogy with known methods.

The present invention also provides a pharmaceutical compositionsuitable for topical administration comprising a PUFA derivative, asdefined herein, or a pharmaceutically acceptable salt, or solvatethereof, and a pharmaceutically acceptable diluent or carrier, for usein treating skin inflammation, as defined herein, in a mammal, asdefined herein.

Preferred pharmaceutical compositions are sterile and pyrogen free.

The pharmaceutical composition is typically in the form of a gel,ointment, cream or lotion.

When said pharmaceutical composition is a gel it typically comprises ahydrophilic polymer such as cross-linked polyethylene glycol,cross-linked starch or polyvinyl pyrrolidone.

An ointment, cream or lotion typically contains an aqueous phase and anoleaginous phase in admixture.

The pharmaceutical composition may additionally contain one or moreemollients, emulsifiers, thickeners and/or preservatives, particularlywhen it is a cream or ointment.

Emollients suitable for inclusion in creams or ointments of the presentinvention are typically long chain alcohols, for example a C8-C22alcohol such as cetyl alcohol, stearyl alcohol and cetearyl alcohol,hydrocarbons such as petrolatum and light mineral oil, or acetylatedlanolin. The total amount of emollient in the pharmaceutical compositionis preferably about 5 wt % to about 30 wt %, and more preferably about 5wt % to about 10 wt % based on the total weight of the pharmaceuticalcomposition.

The emulsifier is typically a nonionic surface active agent, e.g.,polysorbate 60 (available from ICI Americas), sorbitan monostearate,polyglyceryl-4 oleate and polyoxyethylene(4)lauryl ether. Generally thetotal amount of emulsifier is about 2 wt % to about 14 wt %, and morepreferably about 2 wt % to about 6 wt % by weight based on the totalweight of the pharmaceutical composition.

Pharmaceutically acceptable thickeners, such as Veegum.TM.K (availablefrom R. T. Vanderbilt Company, Inc.), and long chain alcohols (i.e.C8-C22 alcohols such as cetyl alcohol, stearyl alcohol and cetearylalcohol) can be used. The total amount of thickener present ispreferably about 3 wt % to about 12 wt % based on the total weight ofthe pharmaceutical composition.

Preservatives such as methylparaben, propylparaben and benzyl alcoholcan be present in the pharmaceutical composition. The appropriate amountof such preservative(s) is known to those skilled in the art. Thepharmaceutical composition may also comprise a fat-soluble antioxidantsuch as ascorbyl palmitate, tocopherol and/or ascorbic acid in thepresence of lecithin.

Optionally, an additional solubilizing agent such as benzyl alcohol,lactic acid, acetic acid, stearic acid or hydrochloric acid can beincluded in the pharmaceutical composition. If an additionalsolubilizing agent is used, the amount present is preferably about 1 wt% to about 12 wt % based on the total weight of the pharmaceuticalcomposition.

Optionally, the pharmaceutical composition can contain a humectant suchas glycerin and a skin penetration enhancer such as butyl stearate, ureaand DMSO. It is known to those skilled in the art that a singleingredient can perform more than one function in a cream, i.e., cetylalcohol can serve both as an emollient and as a thickener.

In one embodiment, the pharmaceutical composition is in the form of acream. The cream typically consists of an oil phase and a water phasemixed together to form an emulsion. Preferably, the cream comprises anoil-in-water emulsion. Preferably, the amount of water present in acream of the invention is about 45 wt % to about 85 wt % based on thetotal weight of the cream.

Where the pharmaceutical composition is in the form of an ointment, ittypically comprises a pharmaceutically acceptable ointment base such aspetrolatum, or polyethylene glycol 400 (available from Union Carbide) incombination with polyethylene glycol 3350 (available from UnionCarbide). The amount of ointment base present in an ointment of theinvention is preferably about 60 wt % to about 95 wt % based on thetotal weight of the ointment.

In the pharmaceutical composition of the present invention, the amountof the PUFA derivative of formula (I) is typically from 0.01 wt % to 50wt %, preferably from 0.5 wt % to 25 wt %, more preferably from 1 wt %to 10 wt %, for example about 5 wt %, based on the total weight of thepharmaceutical composition.

The compound/composition of the present invention is formulated fortopical administration and it may be administered to a patient in anamount such that from 0.00001 to 10 g, preferably from 0.0001 to 1 gactive ingredient is delivered per m² of the area being treated.

Pharmaceutical compositions of the present invention may additionallycomprise one or more corticosteroids as defined herein. The amount ofthe corticosteroid present in the pharmaceutical composition of theinvention is typically 50% or less, preferably 25% or less, morepreferably 10% or less, most preferably 5% or less, of the recommendedamount of said corticosteroid in a commercially available formulation.The skilled person is well aware of the amount of corticosteroidspresent in various topical formulations. For example, the amount ofhydrocortisone present in most commercially available formulations istypically 1% w/w. The amount of clobetasol proprionate present in mostcommercially available formulations is typically 0.0525% w/w.

Thus, pharmaceutical compositions of the present invention typicallycomprise hydrocortisone in an amount of 0.5% w/w or less, preferably0.025% w/w or less, more preferably 0.01% w/w or less, most preferably0.005% w/w or less. Pharmaceutical compositions of the present inventiontypically comprise clobetasol proprionate in an amount of 0.026% w/w orless, preferably 0.013% w/w or less, more preferably 0.0053% w/w orless, most preferably 0.0026% w/w or less.

The pharmaceutical compositions of the present invention typicallycomprise one or more further therapeutic agents, which are notcorticosteroids, as defined herein. The amount of the one or morefurther therapeutic agents, which are not corticosteroids, present inthe composition will be evident to the person skilled in the art.

Pharmaceutical compositions of the present invention may be preparedsimply by admixing the ingredients in a suitable manner.

The present invention also provides the use of a compound which is aPUFA derivative of formula (I) as defined herein or a pharmaceuticallyacceptable salt, or solvate thereof, in the manufacture of a medicamentfor use in treating skin inflammation, as defined herein, in a mammal,as defined herein, by topical administration.

The present invention also provides a method of treating skininflammation, as defined herein, in a mammal, as defined herein, whichmethod comprises administering to the skin of said mammal atherapeutically effective amount of a compound which is a PUFAderivative of formula (I) as defined herein or a pharmaceuticallyacceptable salt, or solvate thereof.

The present invention also provides a pharmaceutical compositioncomprising a polyunsaturated fatty acid (PUFA) derivative of formula(II),

or a pharmaceutically acceptable salt, or solvate thereof, wherein

-   -   -Alk- is —(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH—CH₂-[cis]CH═CH—; and        R₁ is as defined herein;        which composition is for use in treating skin inflammation in a        mammal, by topical administration, and is substantially free of        lithium salts and glucocorticoids.

As the skilled person will appreciate, in this embodiment, thepharmaceutically acceptable salt of the PUFA derivative of formula (II)is not a lithium salt.

Typically, the pharmaceutical composition comprising a polyunsaturatedfatty acid (PUFA) derivative of formula (II) contains the PUFAderivative of formula (II) as sole active ingredient.

Preferably, the pharmaceutical composition comprising a polyunsaturatedfatty acid (PUFA) derivative of formula (II) consists of the PUFAderivative of formula (II) and a pharmaceutically acceptable diluent orcarrier, as defined herein.

Preferably, the PUFA derivative of formula (II) is of formulaR″(C═O)O—CH₂—CH(O(C═O)R″)—CH₂—O(C═O)R″, wherein each R″ is the same andis the aliphatic group of dihommo-gamma-linolenic acid, i.e. R″ is—(CH₂)₆—CH═CH—CH₂—CH═CH—CH₂—CH═CH—(CH₂)₄CH₃, wherein all of the C═Cdouble bonds have cis configuration. Thus, the PUFA derivative offormula (II) is preferably

In a particularly preferred embodiment, R₁ is a hydrogen atom. In thisembodiment, the PUFA derivative of formula (II) is DGLA and isrepresented by the formula

The present invention also provides the use of a pharmaceuticalcomposition comprising a polyunsaturated fatty acid (PUFA) derivative offormula (II) as defined herein in the manufacture of a medicament foruse in treating skin inflammation, as defined herein, in a mammal, asdefined herein, by topical administration, wherein the composition issubstantially free of lithium salts and glucocorticoids.

The present invention also provides a method of treating skininflammation, as defined herein, in a mammal, as defined herein, whichmethod comprises administering to the skin of said mammal atherapeutically effective amount of a pharmaceutical compositioncomprising a polyunsaturated fatty acid (PUFA) derivative of formula(II) as defined herein, wherein the composition is substantially free oflithium salts and glucocorticoids.

EXAMPLES

Immunohistochemistry analyses were carried out to measure the degree ofexpression of COX-2 enzymes in ex vivo porcine ear skin. The COX-2family of enzymes have been strongly linked to inflammation and havebeen found to be present in increased amounts in inflamed tissue. Thus,a decreased level of COX-2 in the skin corresponds with reducedinflammation of the skin.

Example 1

Freshly excised porcine ears were immersed in iced Hank's buffer fortransport from the abattoir to the laboratory. Upon arrival, the porcineears were first washed with running tap water, and the full thicknessskin was liberated from underlying cartilage by blunt dissection using ascalpel and hairs were removed with an electrical razor. The skin wasused within 2 h of slaughter. The full thickness skin was cut intoapproximately 2 cm×2 cm and placed in Hanks balance salt to maintainskin viability.

A 2 mm strip of skin was obtained using a surgical scalpel and the skinstrip then fixed using a 40% formaldehyde solution, dehydrated and setin molten wax. The sections were cut using a Shandon Finesse microtome(Thermo Scientific, Waltham, Mass., USA) to a thickness of 5 μm and wereplaced onto 2.5 cm×7.5 cm×1 mm pre-cleaned microslides. The section ofskin was stained with diaminobenzidine, which binds to COX-2 enzymes andthe slides visualised on a light microscope with image capture facility.

Skin membranes were mounted in Franz diffusion cells using Hanks bufferas receptor phase. Water was used as the donor phase. After 6 hours theskin was removed from the Franz cell apparatus, excess donor phase wasremoved and the skin wiped clean with a clean paper tissue. Thediffusional area was then cut into approximately 2 mm strips using asurgical scalpel and the skin strips then using a 40% formaldehydesolution, dehydrated and set in molten wax. The sections were cut usinga Shandon Finesse microtome (Thermo Scientific, Waltham, Mass., USA) toa thickness of 5 μm and were placed onto 2.5 cm×7.5 cm×1 mm pre-cleanedmicroslides. The section of skin was stained with diaminobenzidine,which binds to COX-2 enzymes, and the slides visualised on a lightmicroscope with image capture facility.

The results of this experiment are shown as FIG. 1. A dark stain ispresent in the sample both after 0 hours and 6 hours, indicating thecontinuing presence of COX-2 in the skin. This indicates that water hasno anti-inflammatory activity.

Example 2

An experiment was carried out as described in Example 1, except that thedonor phase comprised ketoprofen, a known COX-2 inhibitor, in fish oil.

The results of this experiment are shown as FIG. 2. After six hours, theamount of dark stain has reduced, indicating penetration of ketoprofeninto the viable epidermis and activity against COX-2 expression in theskin.

Example 3

An experiment was carried out as described in Example 1, except that thedonor phase comprised a representative compound of the invention, DGLA.

The results of this experiment are shown as FIG. 3. After six hours, theamount of dark stain has reduced, indicating penetration of DGLA intothe viable epidermis and activity against COX-2 expression in the skin.

Example 4

An experiment was carried out as described in Example 1, except that thedonor phase comprised a representative compound of the invention,15-HETrE.

The results of this experiment are shown as FIG. 4. After six hours, theamount of dark stain has reduced, indicating penetration of 15-HETrEinto the viable epidermis and activity against COX-2 expression in theskin.

Example 5

A Western Blotting experiment was carried out to determine the effect oftopically applied representative compounds of the invention DGLA and15-HETrE on the expression of COX-2 in porcine skin. Water was used as acontrol.

The porcine skin membranes (as described in Example 1) were gentlycleaned with de-ionised water before being homogenized (Silverson,Chesham, UK) in a RIPA lysis buffer [50 mM Tris-HCl (pH 7.4), 150 mMNaCl, 1 mM PMSF, 1 mM EDTA, 5 μg mL⁻¹ aprotinin, 5 μg mL⁻¹ leupeptin, 1%Triton X-100, 1% sodium deoxycholate, 0.1% SDS]. After 15 min incubationon ice, the lysates were clarified by centrifugation at 14000×g for 2×15min and the supernatant stored at −80° C. for subsequent proteinanalysis.

Aliquots of 30 μg total protein were separated by SDS-PAGE, transferredto nitrocelullose membranes using the Trans-Blot electrophoreticTransfer Cell and briefly stained with Ponceau S to verify effectivetransfer. Immunoblots were incubated for 1 h in a blocking solution[tris-buffered saline (TBS)-Tween 20 containing 5% (w/v) commercialskimmed milk powder (Marvel) at room temperature. After washing, themembrane was probed overnight at 4° C. with COX-2 antibody at 1:1000,5-LOX at 1:1000 and iNOS at 1:500 in (1:20 and 1:100 western blockingreagent and sodium azide solution respectively made up to volume withTBS tween). Membranes were then incubated for 1 h with HRP-conjugatedanti-rabbit at 1:10000. For β-actin, membranes were probed withanti-actin and anti-mouse for 1 h each at room temperature at 1:10000.After 3×10 min washes in TBS Tween, they were finally exposed to freshlyprepared Dura Substrate for chemiluminescence for appropriate timebefore performing autoradiography.

The results of this experiment are shown as FIG. 5. It can be seen thata significant reduction in COX-2 expression is seen following dosingwith DGLA and 15-HETrE, relative to the control.

1. A compound which is a polyunsaturated fatty acid (PUFA) derivative offormula (I),

or a pharmaceutically acceptable salt, or solvate thereof, wherein -Alk-is —CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—C₃H₆—,—(CH₂)₃—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—,—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)— or—CH₂-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—; R₁ is a hydrogenatom; or R₁ is a C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl, C₆-C₁₃ aryl,5- to 10-membered heteroaryl, C₃-C₇ carbocyclyl or 5- to 10-memberedheterocyclyl group; or R₁ is a group of formula —CH₂—CH(OR₃)—CH₂—(OR₄),wherein R₃ and R₄ are each independently hydrogen atoms or —(C═O)—R₆,wherein R₆ is an aliphatic group having from 3 to 29 carbon atoms; or R₁is a group of formula —(CH₂OCH₂)_(m)OH, wherein m is an integer of from1 to 200; R₂ is a hydrogen atom; or R₂ is a group —(C═O)—R₅, wherein R₅is a C₁-C₆ alkyl, C₂-C₆ alkenyl, C₂-C₆ alkynyl, C₆-C₁₀ aryl, 5- to10-membered heteroaryl, C₃-C₇ carbocyclyl or 5- to 10-memberedheterocyclyl group, or R₅ is an aliphatic group having from 3 to 29carbon atoms; or R₂ is a group of formula —(CH₂OCH₂)_(n)OH, wherein n isan integer of from 1 to 200; and wherein said alkyl, alkenyl, alkynyland aliphatic groups are the same or different and are eachunsubstituted or substituted with 1, 2 or 3 unsubstituted substituentswhich are the same or different and are selected from halogen atoms andC₁₋C₄ alkoxy, C₂₋C₄ alkenyloxy, C₁₋C₄ haloalkyl, C₂₋C₄ haloalkenyl,C₁₋C₄ haloalkoxy, C₂₋C₄ haloalkenyloxy, hydroxyl, —SR', and —NR′R″groups where R′ and R″ are the same or different and represent hydrogenor unsubstituted C₁₋C₂ alkyl; said aryl, heteroaryl, carbocyclyl andheterocyclyl groups are the same or different and are each unsubstitutedor substituted by 1, 2, 3 or 4 unsubstituted substituents which are thesame or different and are selected from halogen atoms, and cyano, nitro,C₁₋C₄ alkyl, C₁₋C₄ alkoxy, C₂₋C₄ alkenyl, C₂₋C₄ alkenyloxy, C₁₋C₄haloalkyl, C₂-C₄ haloalkenyl, C₁₋C₄ haloalkoxy, C₂₋C₄ haloalkenyloxy,hydroxyl, C₁₋C₄ hydroxyalkyl, —SW and —NR′R″ groups wherein each R′ andR″ is the same or different and represents hydrogen or unsubstitutedC₁₋C₄ alkyl; and wherein the PUFA derivative is in the form of aracemate, a stereoisomer or a mixture of stereoisomers, which compoundis for use in treating skin inflammation in a mammal, by topicaladministration.
 2. A compound according to claim 1; wherein R₁ is ahydrogen atom.
 3. A compound according to claim 1 or claim 2, wherein-Alk- is —CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—C₃H₆—,—(CH₂)₃—CH(OR₂)-[trans]CH═CH-[cis]CH═CH—CH₂-[cis]CH═CH—, or—(CH₂)₃-[cis]CH═CH—CH₂—[cis]CH═CH-[trans]CH═CH—CH(OR₂)—.
 4. A compoundaccording to any one of the preceding claims, wherein -Alk- is—(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH-[trans]CH═CH—CH(OR₂)—.
 5. A compoundaccording to any one of the preceding claims, wherein R₂ is a hydrogenatom.
 6. A compound according to any one of the preceding claims,wherein the PUFA derivative is present as the R enantiomer.
 7. Acompound according to any one of the preceding claims, wherein the PUFAderivative is present as the S enantiomer.
 8. A compound according toany one of the preceding claims, wherein the mammal is a human.
 9. Acompound according to any one of the preceding claims, wherein the skininflammation is caused by atopic eczema, contact dermatitis, psoriasisor uremic pruritis.
 10. A compound according to any one of claims 1, 3,4, 6 and 7, wherein: (a) R₁ is a group of formula—CH₂—CH(OR₃)—CH₂—(OR₄), wherein R₃ and R₄ each independently represent ahydrogen atom or —(C═O)—R₅, wherein R₆ is a saturated aliphatic grouphaving from 3 to 29 carbon atoms, wherein at least one of R₃ or R₄ is—(C═O)—R₆; or (b) R₁ is a group of formula —(CH₂OCH₂)_(m)OH, wherein mis as defined in claim 1; and/or (c) R₂ is a group —(C═O)—R₅, wherein R₅is a saturated aliphatic group having from 3 to 29 carbon atoms; or (d)R₂ is a group of formula —(CH₂OCH₂)_(n)OH, wherein n is as defined inclaim
 1. 11. A compound according to any one of the preceding claims,which is co-administered with a corticosteroid.
 12. A compound accordingto any one of claims 1 to 8, 10 and 11, wherein the skin inflammation iscaused by exposure of the skin to electromagnetic radiation.
 13. Apharmaceutical composition suitable for topical administrationcomprising a PUFA derivative, as defined in any one of claims 1 to 7 and10, or a pharmaceutically acceptable salt, or solvate thereof; and apharmaceutically acceptable diluent or carrier, for use in treating skininflammation, as defined in any one of claims 1, 9 and 12, in a mammal,as defined in claim 1 or
 8. 14. A pharmaceutical composition accordingto claim 13, which is in the form of a gel, ointment, cream or lotion.15. A method of treating skin inflammation, as defined in any one ofclaims 1, 9 and 12, in a mammal, as defined in claim 1 or 8, whichmethod comprises administering to the skin of said mammal atherapeutically effective amount of a compound which is a PUFAderivative of formula (I) as defined in any one of claims 1 to 7 and 10or a pharmaceutically acceptable salt, or solvate thereof.
 16. Apharmaceutical composition comprising a polyunsaturated fatty acid(PUFA) derivative of formula (II),

or a pharmaceutically acceptable salt, or solvate thereof, wherein -Alk-is —(CH₂)₃-[cis]CH═CH—CH₂-[cis]CH═CH—CH₂-[cis]CH═CH—; and R₁ is asdefined in any one of claims 1, 2 and 10; which composition is for usein treating skin inflammation in a mammal by topical administration, andis substantially free of lithium salts and glucocorticoids.
 17. Apharmaceutical composition according to claim 16 which contains thepolyunsaturated fatty acid (PUFA) derivative of formula (II) as soleactive ingredient.